1. Field of the Invention
The invention relates to the detection or monitoring of the surface tension of liquids and has particular application to the monitoring of liquids to detect the presence of pollutants. The addition of pollutants to water changes the surface tension of the water. The early detection of pollutants in liquids such as water has become highly important in recent years to aid in meeting state and national pure water requirements. The early detection of pollution caused by accidental spills and equipment failure is critically important in the attainment and continuance of pure water standards. In addition to being effective, pollutant detectors that are low in cost and simple to operate can be installed at many sample points where the high costs of other monitoring devices, e.g., total carbon analyzers have been prohibitive thereby multiplying the effectiveness of the detectors of this invention.
The present invention provides an effective, low cost, simple-to-operate, quick-acting method and device for continuously monitoring the surface tension of liquids and is especially useful in monitoring liquids such as water to detect the presence, if any, of pollutants therein. The method and apparatus of this invention involved the introduction of an inert gas under pressure into the liquid being monitored, decompressing the resulting gas-liquid mixture, and measuring the sound intensity of bubbles which form as a result of the decompression.
2. Description Of The Prior Art
Heretofore, sound intensity has been used to monitor gas-liquid systems by using listening devices to pick up the sound of gas bubbles breaking through the surface of a liquid. U.S. Pat. No. 2,766,838 describes a method of this type in monitoring reactions or changes taking place in solutions such as oxygen release from aqueous solutions of hydrogen peroxide, nitrogen and carbon dioxide release from aqueous solutions of sodium nitrite and urea by the addition of a mineral acid and carbon dioxide release from an aqueous sodium bicarbonate solution by the addition of mineral acid.
U.S. Pat. No. 2,614,645 uses a microphone, amplifier and loudspeaker for detecting the progress of chemical reactions in a reaction bomb.
Additionally, ultrasonic sound has been employed for inspecting and measuring various properties of liquids. U.S. Pat. No. 3,608,715 describes a method and apparatus for detecting particulate matter in liquids in closed containers using ultrasonic sound. U.S. Pat. No. 3,553,636 discloses a system for detecting liquid/liquid interface, viscosity and percent suspended solids in a liquid by utilizing ultrasonic sound.
Various systems and methods have been known heretofore for the determination of surface tension of liquids. U.S. Pat. No. 3,276,844 discloses a system and apparatus for controlling chemical reactions characterized by changes in the surface tension of the reacting mass as the reaction progresses. The system involves the continuous extraction of a sample of the reaction and measuring the pressure required to blow bubbles through the sample.
U.S. Pat. No. 3,854,324 describes a method and system for measuring the clotting time of blood by blowing a train of bubbles into it and detecting changes in the bubble formation characteristics by measuring changes in the pressure required to blow the bubbles.
U.S. Pat. No. 3,426,584 discloses a method and apparatus for measuring surface tension of a liquid by bubbling a gas through two tubes of different radii and placed at different depths in the liquid and measuring the difference in the pressure of flow in the two tubes.
U.S. Pat. No. 3,765,227 discloses apparatus for determining the surface tension of a liquid by measuring pressure differences of a gas in two tubes immersed in the liquid while blowing bubbles through one of the tubes.
U.S. Pat. No. 3,555,783 relates to a method and apparatus for dissolving a gas in a liquid at pressures greater than atmospheric.
None of the above patents, however, relate to a method or apparatus for detecting changes in the surface tension of a liquid or for detecting pollution in a liquid involving the introduction into the liquid of an inert gas under pressure, decompressing the resulting gas-liquid mixture and measuring the sound intensity of bubbles increasing in size during decompression.